Showing papers in "Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment in 1987"

Application of Kalman filtering to track and vertex fitting

Abstract: Recently iterative procedures have been proposed for track and vertex fitting in counter experiments. We show that the proper theoretical framework for these procedures is the theory of linear filtering, in particular the Kalman filter. Using results from filtering theory we confirm and extend the previous results. We also discuss the detection of outliers and of secondary vertices.

New detector concepts

Abstract: On the basis of the semiconductor drift chamber many new detectors are proposed, which enable the determination of energy, energy loss, position and penetration depth of radiation. A novel integrated transistor-detector configuration allows nondestructive repeated readout and amplification of the signal. The concept may be used for the construction of one-or-two-dimensional pixel arrays.

Concept and design procedure for cylindrical element monochromators for synchrotron radiation

Abstract: The design of a new type of soft X-ray grating monochromator which utilizes cylindrical optical elements is proposed. This design is the outcome of a return to simplicity. If not only offers high resolving power and transmission, but also has other advantages over the conventional designs. A simple analytical design procedure (which has been raytracing justified) for designing such a monochromator is described. The raytracing results also confirm that replacement of the cylindrical figure by a spherical one will not degrade the overall monochromator performance.

The achromatic spectrometer LISE at GANIL

Abstract: The achromatic spectrometer LISE installed at GANIL is used for the production and identification of either very neutron- or proton-rich nuclei obtained in the fragmentation of intermediate-energy heavy-ion beams at 0°. The characteristics and advantages of the system are described.

On the Energy Resolution of Uranium and Other Hadron Calorimeters

Abstract: The various components that contribute to the signal from a hadron calorimeter, and the factors that affect the energy resolution with which hadrons can be detected, are examined in detail. The role of the electromagnetic to hadronic signal ratio e h is crucial in this respect. Its value is determined by the Z of the absorber material, the thickness of the passive and active layers, the signal integration time of the detector, and the properties of the readout material, in particular the free proton content and the saturation or recombination properties for few-MeV proton detection. Readout media that contain free protons offer the possibility to tune the e h ratio to the desired value (1.0) through the sampling fraction. Signal equalization ( e h = 1.0) does not seem to be a property unique to 238U, but can also be achieved for lead and even iron calorimeters. The calculations show, on the other hand, that e h values are larger than 1.0 for any calorimeter using liquid-argon readout. The intrinsic energy resolution for hadron detection is largely dominated by fluctuations in the binding energy losses that occur in the nuclear reactions. Efficient neutron detection can considerably reduce these effects provided that energy loss through recoil protons dominates. Calorimeters using 238U, Pb or Fe absorbers, and plastic scintillator, liquid-argon, silicon or TMP readout were investigated. Experimental results on e h values and energy resolution, which are often considered confusing, are nicely reproduced and explained.

Dynamics of electrons in drift detectors

Abstract: The dynamics of electrons generated in silicon drift chambers by ionizing events is studied. Diffusion effects, mutual electrostatic repulsion between the electrons as well as the focusing properties of the depletion field during the electron transport to the anode are considered. The theoretical computations show that the effect of the mutual electrostatic repulsion in the spreading of the charge packet are not negligible even at charge densities produced by a minimum ionizing particle traversing 300 μm of the detector. Experimental results support theoretical expectations.

The first generation of γ-rays from hot nuclei

Abstract: A method to extract spectra of first generation γ-rays from nuclear levels at high excitation energy is described. The reliability and convergence properties of the method are tested on simulated data. Some experimental first generation γ-ray spectra are presented.

A twin ionization chamber for fission fragment detection

Abstract: A twin ionization chamber for fission fragment detection is described. The detector permits measurement of the two fission fragment kinetic energies in an advantageous 2×2 π geometry with an energy resolution of

The momentum-loss achromat — A new method for the isotopical separation of relativistic heavy ions☆

Abstract: The application of the slowing-down process of relativistic heavy ions in a layer of matter in ion-optical devices is theoretically investigated. The modifications of the phase space of the ion beam due to the dissipative forces and the straggling phenomena are discussed. Methods are developed to study the properties of the momentum-loss achromat, an isotope separator consisting of an achromatic magnetic system with an energy degrader located in the intermediate dispersive focal plane. This device separates projectile fragments with respect to A and Z up to uranium over a wide energy range with an efficiency of the order of 50% and with separation times of several hundred nanoseconds.

The physics of radiation damage in particle detectors

Abstract: Intense high-energy particle beams cause damage to semiconductor detectors and signal-conditioning electronics by displacement and long-term ionization effects. While first-principles prediction of effects are not practical, the magnitude of each effect can be scaled approximately between particle energy and type by using an appropriate scaling parameter.

The method of power series tracking for the mathematical description of beam dynamics

Abstract: A new method to compute the properties of charged particle optics systems is presented. It is based on the application of operators and functions to a power series algebra instead of real numbers. The method is as versatile as numerical integration methods and comparable to matrix methods in speed and accuracy thus combining the advantages of both strategies. The method has been implemented through fifth order in the code POWERTRACK. Due to the generality of the method, the order can be increased with very little programming effort.

A new method to measure energy, direction, and polarization of gamma rays

Abstract: A new method to measure the energy, direction, and polarization of gamma rays in the sub-MeV to few MeV range is proposed. We found that the first Compton scattering of the gamma-ray energy degrading process can be correctly reconstructed with a high probability if energies and positions of recoil electrons are recorded with 4–10 keV (rms) and ∼ 1 × 1 × 1 mm 3 for the first 4–5 steps. If a silicon detector stack is used, we get an angular resolution of about 1° (rms) per gamma ray without collimators. We have started development work to make such a device using 2-dimensional silicon strip detectors.

Measurement of the quantum efficiency of TMAE and TEA from threshold to 120 nm

Abstract: Several existing and planned high energy physics experiments incorporate detectors which use either TMAE (tetrakis-dimethylaminoethylene) or TEA (triethylamine) as their photosensitive agent. Understanding the operation of these devices requires knowledge of the absolute photoionization quantum efficiencies and absorption lengths of TMAE and TEA. In an experiment performed at the National Synchrotron Light source at Brookhaven National Laboratory, we have measured these parameters from 120 nm to 280 nm. The quantum efficiencies were normalized to the known photoionization yields of benzene and cis-2-butene. The results of these measurements and details of the experiment are presented in this paper.

GIOS-BEAMTRACE - A program package to determine optical properties of intense ion beams

Abstract: A program package is presented which allows determination of the properties of optical systems for intense ion beams in which space-charge forces must be taken into account. GIOS is based on the algebraic determination of the elements of transfer matrices and allows an automatic optimization of the optical system under consideration. BEAMTRACE is based on the numerical solution of the equations of motion in assumed fields. In both cases the internal space-charge fields are added to the external electromagnetic fields.

Depth-of-interaction determination in NaI(Tl) and BGO scintillation crystals using a temperature gradient

Abstract: A method for determining the depth of interaction in both NaI(Tl) and BGO crystals is investigated. This technique takes advantage of the relationship between temperature and decay time in a scintillation crystal. The depth of interaction is ascertained by measuring the decay time in a crystal with a uniform temperature gradient applied along its depth. The application of determining the depth of interaction in positron emission tomography scanners is discussed.

Radiation damage in silicon strip detectors

Abstract: Silicon strip detectors with 5 μm spatial resolution have been used during 1982–1985 in the ACCMOR spectrometer at CERN. After a local beam flux of about 1014 minimum ionizing particles per cm2 we observe a significant increase in dark current and systematic distortions in the measured coordinates which are explained in terms of a decrease in the effective donor concentration.

Perfomance of a compensating lead-scintillator hadronic calorimeter

Abstract: We have built a sandwich calorimeter consisting of 10 mm thick lead plates and 2.5 mm thick scintillator sheets. The thickness ratio between lead and scintillator was optimized to achieve a good energy resolution for hadrons. We have exposed this calorimeter to electrons, hadrons and muons in the energy range between 3 and 75 GeV, obtaining an average energy resolution of 23% E for electrons and 44% E for hadrons. For energies above 10 GeV and after leakage corrections, the ratio of electron response to hardron response is 1.05.

The resolution of discrepancies in tables of photon attenuation coefficients

Abstract: This paper examines the extent to which theoretical and experimental tabulations of the photon attenuation coefficients are consistent with one another. It sets out the criteria which must apply if accurate measurements are to be made and suggests the manner in which the theoretical data is best combined to give realistic comparisons with experimental data.

A Si strip detector with integrated coupling capacitors

Abstract: A silicon microstrip detector with capacitive coupling of the diode strips to the metallization and with individual polysilicon resistors to each diode has been developed. The detector was tested in a minimum ionizing particle beam showing a performance similar to conventional strip detectors and a spatial resolution of 3.5 μm. Capacitive coupling allows the decoupling of the leakage current from the input to the charge sensitive preamplifier especially in the case of LSI electronics.

Special multipole wiggler design producing circularly polarized synchrotron radiation

Abstract: A planar multipole wiggler device which can produce both linearly and circularly polarized synchrotron radiation is proposed Standard wiggler designs have a quasi sinusoidal magnetic field distribution resulting in a - more or less - perfect cancellation of right/left handed circularly polarized photons emitted from successive poles We show here that one can easily generate a periodic but asymmetric magnetic field distribution having a field integral still equal to zero in order to maintain a straight overall direction of the particle trajectory Due to the asymmetry of the field distribution in our device, the synchrotron radiation along the wiggler axis can keep a high degree of circular polarization above or below the particle trajectory plane As compared to standard bending magnets, the proposed device can afford a significant increase of the available flux of circularly polarized light which is typically proportional to the number of magnetic periods As compared now to the two crossed field undulator system, our wiggler device definitively offers a much broader spectral range of emission and far more flexibility regarding energy scanned experiments which might prove to be very difficult with a two crossed field undulator device The wiggler described here should also accomodate any future or already existing machine with common lattices while a two crossed field undulator system is only to work on very low emittance storage rings

Low capacity drift diode

Abstract: Based on the drift chamber principle a low capacity diode has been built with one large area p+n junction at the front, and p+ and n+ patterns at the rear. The capacitance of the device is only 1.5 pF at an area of 1 cm2 and a thickness of 280 μm. The energy resolution for Am α-particles is 13.5 keV, the optical sensitivity is homogeneous over the whole area, and the charge collection times lie between 10 and 300 ns.

The resolution function of a pulsed-source neutron chopper spectrometer

Abstract: We introduce a formulation for the evaluation of the incident neutron intensity distribution for a chopper time-of-flight spectrometer at a pulsed neutron source. This treatment, incorporated with an assumed scattering function of the sample and the detector geometry, enables calculations of the shape of the time-of-flight intensity profiles of the incident and the scattered neutrons sensed by a neutron detector, thus providing direct comparison with experimental results. The resolution function, R ( Q , E ), is calculated for a nondispersive scatterer at a resonant energy E . The results of the calculations on the basis of this theory are substantiated by measured spectra obtained by the two chopper spectrometers, HRMECS and LRMECS, at the Argonne Intense Pulsed Neutron Source under a variety of experimental conditions. In all cases we find excellent agreement between calculations and experiments. Using these results we present a procedure for the determination of the mean incident neutron energy and the calibration of the energy-transfer scale for pulsed-source chopper spectrometers. These latter do not follow accurately from simple analysis, and are the main objects of this paper.

Performance of the uranium/plastic scintillator calorimeter for the HELIOS experiment at CERN

Abstract: We describe the calorimeter system serving the HELIOS experiment at CERN, its calibration, and its performances measured in test experiments. The calorimeter signal for hadrons was found to be proportional to the energy to within 2% over the energy range 8–200 GeV. Over the same energy range the energy resolution σ E scales as 1 E for both electromagnetic and hadronic showers. The values found were (0.215 ± 0.007) E and (0.337 ± 0.012) E , respectively, for the detection of single particles. The signal ratios e/mip and e π are 0.70 ± 0.05 and 0.984 ± 0.006, where the latter ratio was found to be dependent on the signal integration time the quoted number being obtained for a 130 ns gate. The energy resolution for multiparticle detection was found to be about twice as large as for the detection of single particles in the actual calorimeter configuration. The energy flow logic, designed to provide trigger information on physics quantities such as transverse energy and missing energy, was shown to be very accurate and reliable.

Proton irradiation facility for radiobiological studies at a 7 MV Van de Graaff accelerator

Abstract: This paper describes the proton irradiation facility built up at the 7 MV Van de Graaff accelerator of the INFN-Laboratori Nazionali di Legnaro for radiobiological studies. The system mainly consists of two vacuum chambers, a fast tantalum shutter for intercepting the beam and a beam line containing the beam collimator arrangement and ending with a thin window for the beam extraction in air. Each chamber houses a Ta beam collimator, an Au scatterer foil for the broadening and uniformization of the proton beam over the cell samples and a solicon surface barrier detector for beam monitoring purposes. The test of the facility performance is discussed. With the double scattering system a counting rate in air as low as hundreds of protons per second and a fluence heterogeneity less than 5% within a circular field of 15 mm diameter were obtained. The first results of survival studies of Chinese hamster lung cells (V79-753B) irradiated with a 1.1 MeV proton beam are presented. For comparison, results obtained irradiating the cells with 200 kV X-rays are reported, too.

Development of the SCA/FEL for use in biomedical and materials science experiments

Abstract: The Stanford SCA/FEL system is being modified to be used as a versatile source of photons for a wide range of biomedical and materials science experiments. Characteristics of the FEL beams to be provided are presented, as well as results of recent experiments on energy recovery. A new high brightness injector will be developed and tested, and the possibility of UV operation of an FEL has been assessed, assuming either fundamental or third harmonic output.

The Fréjus nucleon decay detector

Abstract: The characteristics, trigger and monitoring systems, data acquisition as well as the performance of the Frejus nucleon decay detector are presented.

Avalanche semiconductor detector for single optical photons with a time resolution of 60 ps

Abstract: Single optical photons can be detected by semiconductor diodes, that can operate in the triggered avalance mode. Physical properties and structural requirements of such single photon avalance diodes (SPADs) are analyzed. A simple silicon device which has interesting performances (60 ps resolution in single-photon timing, and low dark count rate (less than 10 3 pps at room temperature)) is described. Possible applications are discussed and experimental results are reported (measurements of fast fluorescent decays, and optical time-domain reflectometry in optical fibers with 1 cm resolution). Relations between the device performance and physical phenomena are considered. Criteria are derived for designing and implementing SPAD devices with improved performances. Possible new structures are presented and evaluated.

An ultrahigh-vacuum chamber for surface X-ray diffraction combined with MBE

Abstract: An ultrahigh-vacuum chamber has been built which can be coupled to a diffractometer via a rotary feedthrough. X-rays enter and leave the chamber through a large beryllium window. In addition to standard equipment for surface preparation and reflection high-energy electron diffraction, the chamber contains Knudsen evaporation cells for MBE crystal growth. This arrangement allows in situ diffraction experiments to be performed on growing surfaces and thin films.

Some new developments in the field of high atomic number materials

Abstract: A review is given of room temperature semiconductors used as nuclear radiation detectors including GaAs, CdTe and HgI2. Some new applications are described in the field of dosimetry, spectroscopy and gamma or X-ray imaging.

Thermal neutron cross section and transport properties of polyethylene

Abstract: We report a new measurement of the total cross section of polyethylene at room temperature, for neutrons with energies between 10 −3 and 10 eV. It is shown that a synthetic scattering function is able to produce good agreement with the measured values, as well as with other quantities of interest in moderator design problems. On this basis, thermal neutron diffusion parameters are predicted for polyethylene over a range of useful temperatures.